1. Field of the Present Invention
The present invention relates generally to turbine engine constructions having means for mechanically driving accessories such as pumps, and more particularly to an accessory drive system employing a planetary gear system driving the accessory.
2. Description of the Prior Art
There are many previously known mechanisms for mechanically driving accessories such as fuel pumps, lubricant pumps, cooling pumps, generators and the like, by a turbine engine. Typically, a mechanical transmission is driven by the turbine shaft, and since the speed of the turbine shaft is substantially greater than the speed at which the accessory can be driven, the transmission includes a speed reducer for driving the accessory at a normal operating speed. The transmission speed reducing mechanism often comprises a gear arrangement mounted in a housing which is then secured to the outer casing of the turbine engine. The bulk, weight and size of such mechanisms can substantially increase the bulk, weight and size of the turbine engine installation. Such disadvantages are especially apparent when the gear mounted on the turbine shaft for rotation therewith, is coupled to a driven gear of the transmission which is rotatably mounted about an axis which extends radially outward from the turbine shaft. While such an arrangement permits a turbine accessory to be mounted on the outside of the turbine casing, it substantially increases the breadth and off-axis bulk of the turbine engine installation.
One previously known device which incorporates a speed reduction gear mechanism within the turbine casing itself as shown in U.S. Pat. No. 2,951,631 to Gregory. Gregory discloses a planetary gear system within the compressor stage of a turbine engine. The annular ring gear includes a plurality of blades intermediate the inner and outer peripheries of the ring gear so that the ring gear can be disposed across the fluid inlet of the compressor. Such a construction is disadvantageous for the reason that the planetary gear system effects the flow of fluid through the compressor. In addition, the inclusion of vanes in the gears substantially increases the weight and bulk of the gear. Accordingly, such a construction introduces energy losses which reduce the efficiency of the turbine engine. Moreover, such a complex structure increases the cost and complexity of manufacturing the apparatus.